A strong correlation between the TT(-889) genotype over CC(-889) of the interleukin-1 alpha (IL-1 alpha) transcription regulatory region and age of Alzheimer's disease onset has recently been reported. To determine the functional effects of the genetic variants on plasma protein levels, we cloned the promoter region and determined its activity. The TT genotype significantly increased the transcriptional activity of the IL-1 alpha gene with respect to the CC genotype. A slight increase of the IL-1 alpha mRNA and protein levels was also observed in the plasma.